1. Field of the Invention
The present invention relates to a driving circuit for driving a display device employed in a mobile apparatus such as a hand phone. More particularly, the present invention relates to a driving method adopted in a display device, which has a low power consumption and a small circuit scale, and a driving circuit provided for such a display device.
2. Description of the Related Art
A driving circuit provided for a conventional display device such as a TFT liquid-crystal display is disclosed in Japanese Patent Laid-open No. 2000-66642, which is referred to hereafter as patent reference 1. In order to implement a method of driving the display device, the driving circuit includes gray-scale voltage lines, a decoder, a selector and a gray-scale voltage generation unit. The driving circuit has as many gray-scale voltage lines as gray scales of high-order bits of display data. The decoder is a component for outputting a pulse signal for each time period set in advance for low-order bits of the display data. Receiving the high-order bits of the display data and a pulse signal output by the decoder, the selector selects a gray-scale voltage line corresponding to the high-order bits only during a period in which the pulse signal is in an active state and outputs a gray-scale voltage appearing on the selected gray-scale voltage line to a data line. The gray-scale voltage generation unit is a component for supplying a gray-scale voltage to each of the gray-scale voltage line. The gray-scale voltage varies in accordance with the number of gray scales of low-order bits of the picture display data.
In the configuration and by the operation described above, a display with many gray scales can be obtained by using a driving circuit having a small scale.
With the driving method disclosed in patent reference 1, however, a time period during which a gray-scale voltage appears on the data line is dependent on the display data. Thus, after a gray-scale voltage is output to a specific data line, the gray-scale voltage may be output to a data line adjacent to the specific data line. In such a case, it is quite within the bounds of possibility that the gray-scale voltage output to the specific data line varies so that a desired level of the display luminance cannot be obtained.
In addition, in accordance with the driving method disclosed in patent reference 1, the length of a time period during which a gray-scale voltage appears on the data line is equal to a quotient obtained by dividing 1 scanning period by the number of gray scales of the display-data low-order bits. During such a short fractional time period, it is difficult to change the gray-scale voltage to a desired level.